class Solution {
public:
    string tree2str(TreeNode* root) {
       string str;
       if(root==nullptr)return str;
        str+=to_string(root->val);
       if(root->left||root->right)
       {
        str+="(";
        str+=tree2str(root->left);
        str+=")";
       }
       if(root->right)
       {
        str+="(";
        str+=tree2str(root->right);
        str+=")";
       }

       return str;
    }
};